In an electrocoating process it is essential that metal parts be clean prior to the parts being subjected to electrocoating. Typically, metal parts, such as automobile parts, etc., that are to be electrocoated reach the coating facility with varying degrees of oil on them. These oily parts are placed in a cleaning tank having cleaning solution heated to approximately 120.degree.-180.degree. F. Oil is removed from the parts during this cleaning process. Typically, these cleaning solutions include a surfactant that bonds with the oil and basically prevents removed oil from being redeposited on the parts. However, over time, the surfactant portion of the cleaning solution becomes saturated with oil and is no longer effective in isolating the removed oil from the parts being cleaned. Thus, the cleaning solution is no longer effective to clean the parts.
In the past, the cleaning solution, once saturated with oil, has been rejuvenated in a number of ways. First, it has been standard practice in some operations to shut down the cleaning phase entirely, cool the cleaning solution, and attempt to remove oil off the top of the cleaning solution within the cleaning tank. This is obviously expensive because the cleaning process is interrupted and to that extent the entire electrocoating or coating process is halted.
To avoid costly down time, some electrocoating processors have attempted to continuously drain cleaning solution from the cleaning tank while at the same time replenishing the cleaning tank with fresh or new cleaning solution. This is extremely expensive because it continuously requires that new or fresh cleaning solution be placed in the cleaning tank. It is virtually impossible to incorporate an optimum control in a continuous drain operation. Therefore, it is not uncommon in a continuous drain operation to waste cleaning solution. Also, in a continuous drain approach, one will find that the concentration of the cleaning solution will continue to fluctuate and the fluctuation can be substantial. This can greatly influence the cleaning efficiency of the total operation and often there will be insufficient cleaning solution within the tank and consequently it takes longer to clean the parts or in some cases the parts removed from the tank will not be clean but still have deposits of oil and debris on them.
Also, in prior art processes that involve cleaning oil from metal parts, the entire parts cleaning tank has to be drained periodically. In some processes, for example, the entire cleaning tank and its cleaning solution has to be drained as often as every forty-eight hours. Sometimes this process can consume eight hours and it obviously follows that the cleaning operation performed by the tank has to be completely shut down for the entire period.
Therefore, there is and continues to be a need for an efficient process that will continually remove oil from a parts cleaning solution and which will accomplish that objective without requiring the cleaning process to be shut down and which will provide an economical approach for maintaining and controlling the cost of the cleaning solution.